GASP XXIV. The History of Abruptly Quenched Galaxies in Clusters

The study of cluster post-starburst galaxies gives useful insights on the physical processes quenching the star formation in the most massive environments. Exploiting the Multi Unit Spectroscopic Explorer data of the GAs Stripping Phenomena in galaxies project, we characterize the quenching history of eight local cluster galaxies that were selected for not showing emission lines in their fiber spectra. We inspect the integrated colors, the Hβ rest-frame equivalent widths (EW), star-formation histories (SFHs), and luminosity-weighted age (LWA) maps finding no signs of current star formation throughout the disks of these early-spiral/S0 galaxies. All of them have been passive for at least 20 Myr, but their SF declined on different timescales. In most of them, the outskirts reached undetectable SFRs before the inner regions ("outside-in quenching"). Our sample includes three post-star-forming galaxies, two passive galaxies, and three galaxies with intermediate properties. The first population shows blue colors, deep Hβ in absorption (EW ≫ 2.8 Å), young ages (8.8 < log(LWA (yr)) < 9.2). Two of these galaxies show signs of a central SF enhancement before quenching. Passive galaxies have instead red colors, EW(Hβ) < 2.8 Å, ages in the range 9.2 < log(LWA (yr)) < 10. Finally, the other galaxies are most likely in transition between a post-star-forming and passive phase, as they quenched in an intermediate epoch and have not lost all of the star-forming features yet. The outside-in quenching, the morphology, and kinematics of the stellar component, along with the position of these galaxies within massive clusters (σ_cl = 550-950 km s^-1) point to a scenario in which ram pressure stripping has removed the gas, leading to quenching. Only the three most massive galaxies might alternatively have entered the clusters already quenched. These galaxies are therefore at the final stage of the rapid evolution galaxies undergo when they enter the cluster environment.